Arrangement for electrical heat sealing of packages in a sealing machine



3,008,028 ALING OF Nov. 7, 1961 on VlKAR CHRISTENSSON ARRANGEMENT FORELECTRICAL HEAT SE PACKAGES IN A SEALING MACHINE Filed Nov.

- INVENTOR 00 (IVE/5 7E N.5-$0/Y BY we! ATTORNEY-S United States PatentC) 3,008,028 ARRANGEMENT FOR ELECTRICAL HEAT SEAL- ING F PACKAGES IN ASEALING MACHINE 0d Vikar Christensson, Vikavagan 5, Bromma, Sweden FiledNov. 9, 1959, Ser. No. 851,827 Claims priority, application Sweden Mar.16, 1959 4 Claims. (Cl. 219-19) In the packing of different kinds ofgoods, especially food stuffs, vacuum packages have been used to anincreasing extent, that is, packages of a plastic or similar flexiblematerial which are evacuated and then sealed by heat sealing means. Heatsealing of packages has also been used in cases other than those whereit ha been found advantageous to evacuate the package, such as where thepacked material is so finely divided that it may easily leak out, orWhen it contains liquid ingredients. Usually these packages arecontained in an outer carton of cardboard or similar stifi material andan inner package of a soft plastic or similar material, It is the innerpackage that has been closed and sealed by heat sealing means whichusually comprise electrically heated welding blocks which are pressedagainst the mouth of the inner package.

As the demand for high working capacity of the machines for heat sealinghas increased, these machines have become larger and larger and the timefor starting and stopping them has become longer and longer. During thestarting and stopping time therefore, the machine will run with a speedwhich is lower than normal working speed and each operation of themachine will therefore take a longer time. With regard to the heatsealing, this means that the plastic material of the package is exposedto heat for a longer time than is normally necessary for proper sealing,and tests have been performed which prove that this causes leakypackages as the material tends to melt either fully or partially. In themore serious cases, the melting of the material of the inner packageleaves a large hole. In less serious cases, the material which should beair tight becomes porous, so that the permanency of the package is alsodecreased, although there may not be any way of observing theseimperfections.

The present invention relates to an arrangement which overcomes thedisadvantages of the previous known arrangement.

In the method according to the invention, the heated part used for heatsealing is of such small heat capacity that the amount of heat given offis almost exclusively limited 'by the electrical energy fed thereto, anda time limiting means is connected into the electrical circuit so thatthe amount of energy supplied for each separate operation is limited,

Further details of the invention will be evident from the description inconnection with the attached drawing, in which FIGURE 1 shows aperspective view of a package which is intended to be heat sealed afterevacuation by the method of the invention,

FIGURE 2 shows a cross-section of the heat sealing means, and

FIGURE 3 shows in schematic form a circuit diagram.

In a preferred embodiment of the invention, the package comprises anouter package of cardboard, rectangular in crosssection and having abroad side and a narrow side 11. On each broad side a closing flap 12and 13, respectively, is hinged, and on each narrow side a closing flap14 and 15, respectively, is hinged. The lining has been closed at thebottom in the package of FIGURE 1, and the closing flaps have been bentinwards and glued together. At this time, the package has been provided3,008,028 Patented Nov. 7, 1961 with the material to be packed, and theclosing flaps are folded outwardly at the top so they will not interferewith the handling of the package in the evacuation and sealing machine.Furthermore, the ridge formed at the top by closing of .the lining hasbeen heat sealed along the major part 16 of its length, leaving a smallunsealed portion 17 at one end. It is intended that the package will beevacuated through this unsealed opening.

The package is then placed into a machine for evacuation and sealing ofthe remaining opening 17 by squeezing this opening between a pair ofblocks which are momentarily fed with heat. These blocks have a rathersmall heat capacity, so that no uncontrollable amount of heat isaccumulated on the preceding heating which might cause the package to besubjected to a greater amount of heat at those times when the machine isrunning slowly, although only a normal quantity of electrical energy isfed to the sealing blocks.

The means by which the sealing blocks are brought into contact with themouth of the package do not form part of the present invention. They maybe of any suitable kind and do not require further description.

FIGURE 2 shows a section view through the two welding blocks inseparated position. The block are mounted on a pair of arms 20 and 21,one arm preferably being fixed and the other arm moved into contact withthe month of the package by any suitable means. On the arms 20 and 21are mounted a pair of supporting means 22 and 23, said means beingpartially hidden in the figure by parts placed in front of them. Thesupport means 22 and 23 carry, by means of resilent hinges, a pair offirst means 24 and 25. The hinges consist of binge pins 26 and 27 loadedby means of a spiral or screw spring surrounding them, said springsacting to keep the parts 24 and 25 in the positions shown in thedrawing. The parts 24 and 25, in turn, carry further parts 28 and 29which are connected to the parts 24 and 25 by means of hinges shaped ina similar manner. These are shown in section in FIGURE 2. The hinge pins30 and 31 are surrounded by springs 32 and 33 which act to keep theparts 28 and 29 in the position in the figure. The parts 24, 28 and 25,29 are surrounded by a resistance element in the form of a tape, thisresistance element being of small heat capacity but capable ofgenerating a large capacity of momentary heat when fed with an electriccurrent. The resistance tape is indicated by 34 and 35, respectively. Atone end,

they are connected to the parts 24 and 25, and at this end an electricalconductor, not visible in the drawing, connects the tapes to terminals38 and 39.

The electrical coupling device is shown in FIGURE 3 which also shows theessential parts of the machine in schematic form. This machine is in theform of a turntable having a number of pockets into which the packagesare inserted. The pockets are then closed and sealed and evacuated,thereby removing the air from the inner package to the opening 17. Whenthe package has been sufficiently evacuated the welding blocks arebrought together and heated by an electric current so that the opening17 is sealed.

The turntable is shown schematically at 50in FIGURE 3. In the embodimentillustrated it is divided into twelve pockets, each of which is intendedto handle one package. The pockets are indicated at 51.

The sealing means are schematically shown for only one of the pockets,that is pocket 52, where the above described resistance tapes areindicated by 34 and 35, respectively, as in FIGURE 2. The two resistancetapes 34 and 35 are connected in parallel to a commutator fordistribution of the electrical current pulse at the right moment. Thus,the conductor 53 runs to a commutator larnina 54 in contact with a brush55, and the conductor 56 runs from the other end of the resistance tapeto a commutator rail 57 in contact with a brush 58. The brushes 55 and58 are connected to the secondary Winding of a transformer 61 by meansof conductors 59 and 60. The primary winding of the transformer is fedfrom an available power main of for instance 220 volts. The voltagetransfer in the transformer should suitably be such that a secondaryvoltage of about 2 volts is created when the electrical resistance ofthe resistance tapes is about ohm. This will induce a current of 650amps, or 1300 watts, which causes a sufficiently rapid heating of theresistance bands. The tapes, however, should be fed with current onlyfor a time of approximately of a second, causing a total energy of about15 watt-seconds which corresponds to the most advantageous heating ofthe opening 17.

If the turntable rotates at a rate of 500 turns a minute, then obviouslythe current supply to the resistance tapes would automatically belimited to this period of time because of the action of the commutator.However, during the periods when the turntable is stopped or started andconsequently rotates at a much lower speed, the sealing joints would besubjected to a greater amount of heat and would either be porous or thematerial burned away leaving a hole. The packages which are damaged inthis manner, and in many cases the contents of the packages, would thusbe lost.

To avoid this difficulty a time limiting device 62 is connected in theprimary circuit of the transformer 61. The time limiting device iscontrolled by a pulse contact generator 63 driven by the turntable.

Time limiting devices of this type are well known and should require nofurther description. However, it may be assumed that in its simplestform the arrangement consists of a magnet 64 which, when magnetized,attracts a stop 65 allowing a shaft 66 driven by a clock-Work to startrotating. At the same time, a hook 67 is let down in front of stop 65 sothat the stop cannot return to its normal position until the rotation ofthe shaft causes a pin 68 to displace the hook 67 out of the path ofstop 65. The stop 65 is combined with a contact spring 69 which isconnected into the primary circuit of the transformer 61 so that currentis fed through the primary from the time the electromagnet is energizeduntil the stop has been freed by the pin 68. Obviously, this time can becontrolled with a high degree of accuracy, either by a setting of therotational speed of the clock-work or by setting of the position of thepin 68 on the shaft.

The winding of the electromagnet 64 is connected into a circuit whichalso contains the pulse mechanism 63. This is combined with theturntable 50 so that a pulse is obtained each time a heat sealingoperation is to be started. The pulse mechanism has, in the drawing,been shown as consisting of a pulse disc having teeth 70 which areadapted to activate a level 71 and close the contact 72.

The operation of the arrangement is as follows. After a package has beenintroduced into the turntable in order to be evacuated, the turntablehas rotated a sufficient distance for the evacuation to be completed,the package is then sealed. At this time the pulse contact 72 is closed,and the commutator 54 in cooperation with the brush determines to whichpocket this pulse is guided. The pulse, however, causes immediatestarting of the time limiting mechanism 62, which, during a given time,will feed primary current to the transformer 61 by means of the contact69. At the same time the transformer is feeding secondary current overthe conductors 59 and to the commutator 5457 for distribution to theheat sealing means 34 and 35 of the selected pocket. These heat sealingmeans will therefore receive an amount of electrical energy which isdependent upon the voltage of the transformer, the resistance of theresistance tapes, and the time setting of the time limiting device 62.The amount of electrical energy delivered is therefore independent ofthe speed with which the turntable rotatesi What is claimed. is:

1. Apparatus for heat sealing of packages comprising a turntable havinga plurality of pockets each adapted to receive a package, means forrotating said turntable, a pair of opposed sealing means disposed withineach of said pockets, means for bringing said sealing means into contactwith the opening in a package disposed in said pocket, said sealingmeans including a resistance element adapted to be heated by an electriccurrent, a source of electrical energy, commutator means fordistributing electrical energy to said sealing means in a preselectedone of said pockets, and means for limiting the amount of electricalenergy delivered to each of said sealing means.

2. Apparatus according to claim 1 wherein said limiting means includes atransformer and a device for limiting the time during which electricalenergy is fed through said transformer.

3. Apparatus according to claim 2 including means actuated by rotationof said turntable for controlling said time limiting device.

4. Apparatus according to claim 3 wherein said control means includes atoothed disc rotating on the same shaft as said turntable.

Langer t Mar. 3, 1953 Lyijynen Jan. 13, 1959

